This invention relates to a method of applying to a gravure cylinder a plating of copper especially adapted to receive electronic engraving. In this form of engraving a diamond tip stylus is forced against a copper outer layer to make an ink-receiving impression.
Copper plating applied to gravure cylinders with sufficient leveling tends to have an amorphous grain structure. Such a structure, because it lacks the requisite hardness or perhaps because of its amorphous nature, is not suitable for electronic engraving. According to an article published in Gravure by Ettl and Kolbinger, it is believed that exceptional hardness is required for successful electronic engraving. To date, typical prior art processes for obtaining such a satisfactory copper deposit must be so nearly chloride ion free that special reagents and de-ionized water are required for the make-up bath.
Applicants have determined that a finely grained laminar deposit, even though lacking the hardness generally believed to be necessary for electronic engraving, is highly suitable for use in such an engraving process. Achieving successful engraving at a lower degree of hardness is an advantage in that it reduces tool wear and prolongs the useful life of the apparatus. Applicants' laminar deposit is achieved through the use of a bath containing the usual sulfate and copper ions, but containing an additive whose ingredients are specifically identified and carefully balanced.
The copper plate developed from the bath of this invention is laminar in form and characterized by layers or crystal structure changes having an approximate thickness of 0.00005 inches which are readily visible under an optical microscope when the plate is sectioned and etched.